A variety of diseases exists that require regular treatment by injection or infusion of a medicament with a medical device that ejects this medicament. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses, for example once or several times per day. For instance, a pre-filled disposable insulin pen can be used as an injection device. Alternatively, a re-usable pen may be used. A re-usable pen allows replacement of an empty medicament cartridge by a new one. Either pen may come with a set of one-way needles that are replaced before each use. The insulin dose to be injected can then for instance be manually selected at the insulin pen by turning a dosage knob and observing the actual dose from a dose window or display of the insulin pen. The dose is then injected by inserting the needle into a suited skin portion and pressing an actuation button of the insulin pen.
It is desirable to provide such medical devices for ejection of medicaments with functionality beyond their basic medicament ejection capabilities, such as for instance functionality to monitor use and/or to prevent false handling (for instance untimely reuse) of the medical devices. This requires detection of actuation actions performed with the medical device.
International patent application publication WO 2007/107564 A1 discloses a method and an electronic module for monitoring the operation of a medication delivery device. An electronic module is releasably arranged in the vicinity of the medication delivery device and used to detect measurable acoustical or vibrational signals generated in response to an action occurring within the medication delivery device. Information associated with or representing the measured signals is then stored.
However, such measurement of acoustical signals (such as for instance sounds generated when dialling or ejecting a dose) may not be reliable enough in noisy environments. The same holds for the detection of vibrational signals in mobile environments.